The invention relates to a system for automatically loading semiconductor wafers into a diffusion furnace, and particularly to such a system which uses non-articulated, rather than articulated, robotic members, is not overly complex in structure, and is relatively inexpensive compared to commercially available automatic loading systems for loading wafer boats onto cantilever paddles.
The present assignee has marketed a simplified automatic wafer loading system for loading slotted cantilever tubes of the type described in U.S. Pat. No. 4,543,059, using the trademark ATMOSCAN. That automatic wafer loading system is much simpler in construction and lower in cost than automatic wafer loading systems ordinarily used for loading wafer boats into diffusion furnaces. One known system for loading a number of loaded wafer boats onto a silicon carbide cantilever "paddle" is marketed by PRI, Inc. (Precision Robotics, Incorporated). This system includes articulated "hand", "arm", and "shoulder" elements to load wafer boats onto a silicon carbide paddle. The PRI system also has the capability of storing information regarding locations of wafer boats, locations of test wafers in each wafer boat, and separately identifying and loading test wafers. The PRI system is marketed for $400,000-$500,000. Another complex prior art wafer loading system is marketed by Tokyo Electron Limited, and sells for $600,000-$700,000. Most of the available systems for loading wafer boats onto cantilever paddles use the articulated arm members to carry a wafer boat transversely and directly to the desired location on the cantilever paddle.
The above-mentioned non-articulated ATMOSCAN cantilever tube loading system mentioned above includes a queue assembly that moves on a base. The base also supports a track on which a carriage supporting the cantilever tube moves. "Shell" type wafer boats, which typically carry 25-50 wafers, are manually loaded onto a queue rack. A "queue carriage" lifts the next available wafer boat off of the queue rack and carries it to a vertical elevator having a pair of "fork lift" tines which engage the bottom of the wafer boat and lift it off of the "queue nest". The elevator is operated under computer control. The computer is programmed to raise the wafer boat to the level of one of four desired wafer loading assemblies. A telescoping arm supports the tines, and moves transversely to the longitudinal axis of the ATMOSCAN cantilever tube, carrying the wafer boat into precise alignment with such longitudinal axis. An IBAL (Individual Boat Automated Loading) assembly is mounted on a carriage that moves along the same track as the carriage that supports the cantilever tube. The IBAL assembly includes a centered lift or "nest" mechanism aligned with a loading slot in the bottom surface of the cantilever tube. That lift mechanism is narrower than the slot, and lifts the wafer boat off the tines and carries it into the open end of the slotted cantilever tube; the lift or "nest" mechanism extends through the loading slot to accomplish this.
Still under programmed control, the IBAL assembly carries the loaded wafer boat into the next available wafer boat position inside the cantilever tube. The IBAL assembly then lowers the wafer boat onto the bottom inside surface of the cantilever tube so it covers part of the tube of the loading slot. The IBAL assembly then moves back to its initial position and waits for another loaded wafer boat to be delivered by an elevator assembly.
The foregoing prior art system is subsequently described in more detail with reference to FIG. 1, which also illustrates the present invention for loading a cantilever paddle.
By way of background, there are many existing wafer fabrication facilities in wafer fabrication facilities throughout the world. Most such wafer fabrication facilities have been designed with a fixed amount of floor space for each diffusion furnace and its associated wafer loading station. Such fixed amounts of floor space often are not large enough to accommodate the large, complex, expensive automatic cantilever paddle wafer loading systems of the type marketed by PRI and Tokyo Electron Limited. In recent years, there has been a substantial increase in the number of new semiconductor wafer fabrication facilities being constructed. The new wafer fabrication facilities allocate larger amounts of floor space for each furnace station (thereby increasing the overhead cost for each furnace) in order to accommodate the larger automatic wafer loading systems of the type marketed by PRI, Tokyo Electron Limited, and others. The new wafer fabrication facilities constitute the main market for such wafer loading systems.
However, there is an unmet need for an inexpensive, effective automatic system for loading wafer boats onto cantilever paddles which can fit into the limited amount of space available for loading stations in the already existing wafer fabrication facilities. There are substantial reasons favoring use of automatic wafer boat loading systems for each furnace station in any wafer fabrication facility, including avoiding safety problems that are associated with operators manually lifting heavy boatloads of semiconductor wafers high enough to place them on the cantilever paddle for the top furnace tube of each furnace station, and reducing the number of yield-reducing human-produced particulates that inevitably are generated by every human-performed task in semiconductor wafer processing. Up to now, however, no one has been able to provide a system that meets the needs of this market at an acceptable cost.